The present invention relates to a flexible foamed product with skin and a process for manufacturing such a product.
A two solution-reacting type urethane paint (a two-pack urethane paint) has been known as a skin composition which gives a highly chemical-resistant skin for a flexible foamed product. The skin obtainable from this paint, however, is usually lacking in elongation and flexibility; is poor in light-fastness and heat resistance; its elongation drops greatly and its discoloration is great after an aging test. When the reactivity of the two solutions-reacting type urethane paint is increased, it has the drawback that its pot life is reduced and its storage stability is decreased; but if its reactivity is decreased, its curing time is extended and as a consequence the number of molds which must be employed for molding is increased, resulting in an increased cost.
Also, as a paint with good workability and productivity which yields a highly flexible skin, a one solution type urethane paint which is a linear urethane polymer dissolved in an organic solvent has been known, but the skin obtainable from this paint, as might be expected, possesses poor resistance to solvents and chemicals and its physical properties after light-fastness tests are poor. Some of these drawbacks of the linear urethane polymer may be eliminated by increasing its molecular weight and its intermolecular entanglement (method "a") , but this method gives an insufficient improvement in chemical resistance and with this method a sprayed paint often leaves a trail. Therefore, in order to obtain a good skin the nonvolatile content of paint (NV-value) has to be substantially reduced. Another method (b) is available for this purpose, according to which a component of linear urethane polymer, mainly isocyanate, is replaced with a component which is, for example, more chemical-resistant. However, the skin obtainable in this case is usually intensely yellowed after light-fastness and heat resistance tests and dimethylformamide (DMF), which has a strong dissolving power and gives a harmful effect on the human body, must be used as the solvent for the paint. DMF produces an unfavorable work environment, evaporates slowly and takes a long time to dry.
A third method (c) is available, according to which a bifunctional or polyfunctional active isocyanate is employed for bridging the linear urethane polymer, but since the solvent of the linear urethane polymer usually contains an alcoholic solvent, the --OH group in the solvent and isocyanate react with each other, shortening the pot life and making the paint less workable. If a nonalcoholic solvent is selected to avoid this drawback, the solvent used must be DMF, which results in the same drawbacks that are noted above. Moreover, the active isocyanate is highly noxious to the worker and produces a bad environment for working and leads to low productivity.
What has been described above is summarized in Table 1, except that methods a, b, c and d are referred to as "remedys" a, b, c and d.
TABLE 1 __________________________________________________________________________ Two solutions-reacting PAINT urethane paint One solution type urethane polymer lacquer Reactivity Reactivity ITEM REMEDY low high No remedy Remedy a Remedy b Remedy __________________________________________________________________________ c Physical Elongation Properties (Flexibility) .DELTA. .about. X .DELTA. .about. X .circle. .circle. .circle. .circle. .about. .DELTA. Elongation Light-fastness retained .DELTA. .about. X .DELTA. .about. X .DELTA. .circle. .about. .DELTA. .DELTA. .circle. .about. .DELTA. heat resistance Discoloration .DELTA. .about. X .DELTA. .about. X .circle. .circle. .DELTA. .about. X .circle. Chemical-resistance .circle. .circle. X X .about. .DELTA. .circle. .about. .DELTA. .circle. .about. .DELTA. Anti-scratch strength .DELTA. .about. X .DELTA. .about. X .circle. .circle. .circle. .circle. Productivity: Sprayability .circle. .circle. .circle. X .circle. .circle. etc. Storage stability .DELTA. X .circle. .circle. .circle. X Cycle time X .circle. .circle. .DELTA. .DELTA. .DELTA. Work environment .DELTA. .DELTA. .circle. .circle. X XX __________________________________________________________________________ Note: .circle.--- good .DELTA.--- fair X--- poor